Stationary systems, and in particular, stationary computer systems are normally coupled to a wall outlet that provides 60 Hz AC power. Since a variety of power line failures may cause a computer system to power down in an uncontrolled manner, a computer system with high reliability and a guaranteed ON time requirement may use an Uninterruptable Power Supply (UPS). In order to improve performance, computers are increasingly using write back caches, which means that updated data intended for the disk is temporarily stored in RAM. If a power failure occurs, there is more of a chance that new data will be lost, thus UPS systems are becoming important for all computers.
A UPS is a backup power system used when the electrical power line fails or drops to an unacceptable voltage level. Small UPS systems may only provide power from a battery for a few minutes which is enough to power down the computer in an orderly manner. Sophisticated systems are tied to electrical generators that can provide power for days. A UPS system may be connected to a file server so that, in the event of a problem, all network users may be alerted to save files and shut down immediately. There are a variety of UPS systems, an online UPS, a standby or offline UPS, and a line interactive UPS. An online UPS provides a constant source of electrical power from the battery, while the batteries are being recharged from AC power. A standby UPS normally draws current from the AC outlet and switches to battery within a few milliseconds after detecting a power failure. The line interactive UPS is a hybrid of the online and standby units. Like the standby, it does not constantly draw from the battery, but it switches to battery faster when required. In addition, the line interactive unit does not use the battery when low voltage is encountered. It uses extra power from the AC source to make up the difference in voltage. Since most all computer systems use AC power as its primary input, the UPS system also couples AC power to the computer using the same type of AC power cable that normally plugs into a wall outlet.
A UPS system is a separate unit and must communicate with the computer that it is powering, for example, if it senses a problem with the primary AC line voltage. This communication is normally done using a RS232 or Universal Serial Bus (USB) protocol. This requires the UPS and the computer to have a separate data cable with connectors and a UPS side receptacle for the data cable in order for the information from the UPS system to be coupled to the computer. This separate data cable and connector and any required RS232 or USB drivers and receivers may add cost to the computer system and the UPS as well as using a port input that could be used for another input/output (I/O) device.
There is, therefore, a need for a method and an apparatus to allow a UPS system to communicate to the computer it is powering without the addition of RS232 or USB circuitry, cable, and required port connection.